correct README

Usecases/README.md

@@ -59,6 +59,9 @@ copy one of the existing cases into a new file and start working on your own.
  It might happen, that not all usecases are running, due to forgetting to update
 the script. If that happens and you wanted to run that particular usecase,
 find a usecase that works and diff the two files, to see what's missing.
+Usually a parameter that has been later on during development is missing so
+that the simulation complains of missing parameters or unknown variables.
+**Sigh**. It is what it is.
 >>>
 
 To understand how usecases are set up, let's have a look at the file